1. Field of the Invention
The present invention relates to the field of power management for VoIP and SLIC/CODEC.
2. Prior Art
In SLIC (subscriber line interface circuit) operation, different line states work with very different voltage and current load conditions in a totally event driven fashion. For instance, the phone will be in a ringing state until someone picks up the phone, then the line switches to the Active state. A pulse width modulated (PWM) power supply controller needs to adjust the output voltage/load change due to state change on the fly with minimal ripple produced in the line voltage. This is very challenging, since large load changes tend to produce voltage fluctuations. The present invention resolves PWM line supply ripple problems arising from undershoot and overshoot due to the high range of dynamic load switching coupled with large voltage changes of the DCDC converter in VoIP (voice over Internet protocol) SLIC applications. In general SLICs, the voltage/current requirements of an SLIC is line state dependent, and has a range from as low as 6V to as high as above 100V as standard requirements. The load current requirements are from as low 100 uA to 100 mA. Within this wide range of power regulation, a PWM DCDC converter needs to be fast and accurate with minimal ripple within a very stringent range such as 100 mV or less for good idle channel noise performance and voice quality. Therefore it is difficult to satisfy the dynamic load requirements, yet maintain a high quality ripple specification.
Various PWM DCDC algorithms have been proposed in the past. Typically they are confined to very specific applications, mostly fixed voltage with dynamic load current conditions or fixed load current and dynamic voltage swings. They are not designed for dynamic VoIP SLIC line state switching. The overshoot and undershoot requirements and external boost and buck of the prior art are not the same as required by VoIP SLIC application.